#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
int xt2_4(){
	int count = 0;
	while (1){
		int n = 0;
		int m = 0;
		scanf("%d", &n);
		scanf("%d", &m);
		if (n == m&&n == 0){
			break;
		}
		count++;
		double sum = 0;
		for (int i = n; i <= m;i++){
			sum += 1.0 / i / i;
		}
		printf("Case %d:%.5f\n",count,sum);

	}
	return 0;
}